R devel - Aug 2008 - '"ts" treated as a registered S3 class, but keep its "structure" behaviour' ?

Dear all,

In R-devel I have noticed the new approach for the "ts" class in the
package "methods".

the "structure" behaviour of "ts" is not always kept when
one uses
"ts" objects and objects of classes which extend the virtual class
"structure".

As a short example:

## this works fine
setClass("foo", representation(header = "character"),
contains = "structure")
foo <- new("foo", 1:10, header = "foo")
ts <- ts(1:10)
foo / ts

## but the problem appears when one defines an "Ops" method for class
"foo"
setMethod("Ops", c("foo", "foo"),
           function(e1, e2) {
               .Data <- callGeneric(e1 at .Data, e2 at .Data)
               header <- paste(e1 at header, e2 at header, sep =
"_")
               new("foo", .Data, header = header)
           })
foo <- new("foo", 1:10, header = "foo")
foo + foo
ts <- ts(1:10)
foo / ts
# Error in getDataPart(1:10) : no '.Data' slot defined for class
"ts"

Is this the expected behavior?

regards,
Yohan

--
PhD student
Swiss Federal Institute of Technology
Zurich

www.ethz.ch

Yohan Chalabi wrote:
> Dear all,
>
> In R-devel I have noticed the new approach for the "ts" class in
the
> package "methods".
>
> the "structure" behaviour of "ts" is not always kept
when one uses
> "ts" objects and objects of classes which extend the virtual
class
> "structure".
>
> As a short example:
>
> ## this works fine
> setClass("foo", representation(header = "character"),
contains = "structure")
> foo <- new("foo", 1:10, header = "foo")
> ts <- ts(1:10)
> foo / ts
>
> ## but the problem appears when one defines an "Ops" method for
class "foo"
> setMethod("Ops", c("foo", "foo"),
>            function(e1, e2) {
>                .Data <- callGeneric(e1 at .Data, e2 at .Data)
>                header <- paste(e1 at header, e2 at header, sep =
"_")
>                new("foo", .Data, header = header)
>            })
> foo <- new("foo", 1:10, header = "foo")
> foo + foo
> ts <- ts(1:10)
> foo / ts
> # Error in getDataPart(1:10) : no '.Data' slot defined for class
"ts"
>
> Is this the expected behavior?
>   
No, not expected.  It may take some special treatement to fix it, though.

Your subject heading is indeed the problem.  Normally, the structure of 
an S3 class is a black box, and no S4 slots should usually be associated 
with it when it's registered via setOldClass.

However, just because "ts" does want to be a "structure"
class, it would
be nice to give it a .Data slot.  I'll experiment with this and see if 
it causes other things to break immediately.

Thanks for the report.

John Chambers
> regards,
> Yohan
>
> --
> PhD student
> Swiss Federal Institute of Technology
> Zurich
>
> www.ethz.ch
>
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